Exogenous phytases have the capacity to increase the nutritional value of animal feeds through the hydrolysis of phytate-bound phosphorus. Inorganic trace minerals (ITM) routinely added to feed can negatively impact phytase activity. Recent research has shown that replacement of ITMs with organic trace minerals (OTMs) may overcome these inhibitory effects due to their greater levels of stability. The objective of the present study was to assess the effects of ITMs and OTMs on the enzyme activities of five different commercial phytases. Exposure to copper sulphate (ITM) greatly inhibited phytase activity compared to OTMs, at reflective inclusion levels. Similarly, exposure to iron sulphate (ITM) had a greater effect on phytase activity than OTMs, at reflective inclusion rates. The observed responses were instigated by trace mineral source, elemental concentration and phytase mode of action. Additional studies assessed the effects of simulated mineral mixes containing sequentially added copper, iron, zinc, and manganese. Similar to previous findings, exposure to ITM mixes resulted in high losses of phytase activity (85 – 95 %). Comparatively, considerably more phytase activity was retained with OTM mixes (55 – 80 %). Interestingly, diverse activity retentions were observed after the exposure of phytase to commercial organic premixes (20 – 80 %), further indicating that the classification of OTM was a key determinant of phytase function. The effect of pH changes, reflective of the poultry gastrointestinal tract (GIT), on the activity of a 3- and 6-phytase in the presence of mineral mixes was assessed. Once again, OTMs had greater enzyme retention for both phytases. Unlike the 3phytase, 6-phytase was dependent on pH, again emphasising that phytase mode of action was integral for activity retention. Findings from the present study indicated that the retention of exogenous phytase function was dependent on trace mineral source. These responses differed between individual minerals and phytases, an important formulation consideration for maximising feed quality.